In a conventional galvanizing operation, the article sought to be plated is first dipped in a bath of cleaning fluid, and is thereafter dipped in a bath of molten zinc. The zinc bath, in turn, is contained in a steel pot or "kettle" enclosed by refractory material to form a fire box.
It is essential that the kettle be heated to a temperature great enough to completely melt the zinc. However, the temperature must also be held below about 870 degrees F., or the molten zinc will engage in a deteriorating interaction with the steel wall of the kettle. In this respect, it should be noted that this interaction is as much a characteristic of zinc as it is a characteristic of the temperature. Furthermore, the rate of heat transfer between the interior of the fire box and the zinc is a function of the exterior area of the wall of the steel kettle.
Zinc and silicon are also especially interactive at these temperatures, and therefore it has always been the practice to fabricate these kettles from steel having a very low silicon content. Until recently this was not a problem, because most steels have previously been made by the conventional "open-hearth" process which provides steel having a very low silicon content. Now, however, most steels are produced using the new "continuous casting technique, wherein the steel tends to have a much higher silicon content.
This shift within the steel-making industry, from open-hearth to continuous casting, has tended to create a problem for the galvanizing industry with regard to replacing these kettles as they burn out over time. Some steel will always be produced using the open-hearth process, of course, and it is also possible to produce steel with a lower silicon content on special order using the continuous casting process. Notwithstanding, it will be readily apparent that the technological improvements in the steel industry have created a shortage in the type of steel needed by the galvanizing industry.
These problems have been overcome by the present invention, however, and improved kettles are now provided which may be conveniently fabricated from steels having a higher silicon or carbon content than has heretofore been tolerable for galvanizing purposes.